The synthesis of a fluorescence carrier, 4-allyloxy-7-aminocoumarin (AAC) having terminal double bond for preparing an optical chemical sensor has been described. The carrier is covalently immobilized on a quartz glass plate surface treated with a silanizing agent to prevent its leakage. The AAC based sensor can be applied for indole-3-acetic acid (IAA) assay by fluorescence quenching. The quenching process and the basis of quantitative assay were discussed. The experimental conditions for IAA assay has been optimized. The AAC sensor shows a linear response toward IAA in the concentration range of 1.0×10-6 to 1.0×10-3 mol l-1, with a detection limit of 9.0×10-7 mol l-1 at pH 7.0. The AAC sensor has good selectivity for IAA over many inorganic and organic compounds.